1. Field of the Invention
The present invention generally relates to a high-frequency module and a radio device including the same, and more particularly, to a high-frequency module for use in a balanced transmitter/receiver system, and to a radio device including the same.
2. Description of the Related Art
In general, the 2.4 GHz band is an Industrial, Scientific and Medical (ISM) equipment frequency band, and is internationally allocated for industrial, scientific and medical use so as to prevent disturbances due to crosstalk or interference. The 2.4 GHz is utilized for wireless local area networks (LANs) because it ensures the bandwidth in which high-speed broadband communications of several megabits per second (Mbps) are possible, or because it has high availability and high radio-wave propagation at low cost.
FIG. 13 is a block diagram showing a radio frequency (RF) circuit for Bluetooth, a wireless LAN protocol, which was suggested in “NIKKEI ELECTRONICS” No. 761, p. 155, published by Nikkei Business Publications, Inc. The RF circuit includes a band-pass filter 51, a high-frequency switch 52 for switching a transmission signal and a reception signal, a transmitter circuit Tx having a high-power amplifier 53 and a multiplier 54, and a receiver circuit Rx having a low-noise amplifier 55 and a mixer 56. The band-pass filter 51 attenuates spurious high-frequency signals such as transmission and reception signals of other frequency band communication systems represented by GSM (Global System for Mobile communication) in the 900 MHz band, DCS (Digital Cellular System) in the 1.8 GHz band, and PCS (personal Communication Services) in the 1.9 GHz band, and the second and third harmonics of reception signals of the 2.4 GHz band communication system of the present invention. The band-pass filter 51 has a first terminal 511 connected to an antenna ANT, and a second terminal 512 connected to a first terminal 521 of the high-frequency switch 52. A second terminal 522 and a third terminal 523 of the high-frequency switch 52 are connected to the high-power amplifier 53 in the transmitter circuit Tx, and the low-noise amplifier 55 in the receiver circuit Rx, respectively.
In the above-described RF circuit, the band-pass filter is used as a high-frequency filter for attenuating spurious high-frequency signals such as transmission and reception signals of other frequency band communication systems, and the second and third harmonics of reception signals of the communication system of the present invention. Such a typical RF circuit experiences problems with the insertion loss at the high-frequency filter being reduced, thus reducing the insertion loss at a high-frequency module.